1. Field of the Invention
The present invention relates to sealing devices for the mobile elements of artillery recoil brakes.
2. Description of the Prior Art
It is known that an artillery gun includes:
a recoiling mass consisting essentially of the tube-breech assembly;
a recoil brake placed between the recoiling mass and the gun mount, and which usually operates hydraulically;
a filling device to remedy any fluid leakage that may appear in the brake, and to keep the assembly under constant pressure, generally on the order of a few bars, when at rest;
a counterrecoil device that stores a part of the recoil energy and returns it later to the mobile assembly to return it to battery position, ready for a new shot.
Several principles of hydraulic recoil brake operation are known. The most commonly used are:
brakes with liner sleeves (FIG. 1);
brakes with counteracting rods (FIG. 2).
In both cases, these brakes consist of a piston 1 sliding inside a cylinder 2, which is filled with a fluid (most often oil). The piston therefore defines one annular chamber 4 and one cylindrical chamber 5 inside the cylinder. These chambers will hereafter be referred to as the high-pressure and low-pressure chambers, respectively.
The fluid is used to decelerate the relative motion of the piston and cylinder. The rate deceleration depends on the geometry of a fluid passage between the high- and low-pressure chambers. The seal between the cylinder cap and the piston rod at the exit hole is provided by a seal 6.
In the case of a sleeve liner (FIG. 1), the passage consists of a variable-section cutout 3 in the sleeve liner.
In the counteracting rod brake design (FIG. 2), the means of communication consists of a combination of constant-geometry orifices 8 and 9 and of a variable-diameter counteracting rod 10. This counteracting rod, to the extent that it blocks more or less the orifice, varies the section of the oil passage between the two chambers and therefore the rate of deceleration.
The piston and cylinder may, according to the configuration, be integral with the craddle or slide, or integral with the recoiling mass of the gun. The sectional area of the oil passage between the two chambers, and therefore the rate of deceleration, can be calibrated as a function of the recoil distance travelled. Generally at the start of the recoil, during the time the projectile is travelling through the tube, a nearly zero braking force is desired, in order not to apply forces to the mobile mass that might harm the accuracy of the shot. This is called the "free recoil" phase.
As the sectional area of the oil passage varies, a deceleration is gradually obtained, which will be accompanied by a rise in the pressure in chamber 4 which will increase as the allowable recoil distance decreases.
A common problem of these types of brakes resides in the difficulty of finding the right seals 6. These seals must withstand very severe pressure stresses of the order of 400 bar while the rod may be moving at speeds of up to 20 m/s, under temperature condition ranging from -30.degree. C., to -55.degree. CC.
Few commercially available seals can meet such specifications, which limits the choice of them and increases costs.
Furthermore, knowing that the braking force can be expresed by the formula F=P.S, in which P is the maximum pressure in the chamber 4 and S the active sectional area of piston 1, it can be seen that if any increase has to be made in the recoil force to be absorbed, the only way to do this is to increase the diameter of the brake, since the maximum allowable pressure is limited. Yet it would be advantageous to be able to decrease this diameter without increasing the pressure on the seal at the same time, as this would reduce the weight and dimensions of the brake.
Similarly, for a given diameter, the reduction of this pressure would make it possible to use seals of common quality, costing little and easy to procure and replace.
It is the purpose of the present invention to propose a sealing device that will remedy the disadvantages mentioned above.